Power amplifier adjustment for transmit beamforming in multi-antenna wireless systems

ABSTRACT

One or more beamsteering matrices are applied to a plurality of signals to be transmitted via multiple antennas. The plurality of signals are provided to a plurality of power amplifiers coupled to the multiple antennas after applying the one or more beamsteering matrices to the plurality of signals. Signal energies are determined for the plurality of signals provided to the plurality of power amplifiers, and output power levels of the plurality of power amplifiers are adjusted based on the determined signal energies.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 60/913,936, entitled “Power Amplifier (PA) Backoff forTransmit Beamforming in Multi-Antenna Wireless Systems,” filed on Apr.25, 2007, which is hereby incorporated by reference herein in itsentirety.

FIELD OF TECHNOLOGY

The present disclosure relates generally to wireless communicationsystems and, more particularly, to an apparatus and method for varyingthe power of amplifiers in a multi-antenna transmitter in conjunctionwith transmit beamsteering.

DESCRIPTION OF THE RELATED ART

An ever-increasing number of relatively cheap, low power wireless datacommunication services, networks and devices have been made availableover the past numbers of years, promising near wire speed transmissionand reliability. Various wireless technology is described in detail inthe 802.11 IEEE Standard, including for example, the IEEE Standard802.11a (1999) and its updates and amendments, the IEEE Standard 802.11g(2003), as well as the IEEE Standard 802.11n now in the process of beingadopted, all of which are collectively incorporated herein fully byreference. These standards have been or are in the process of beingcommercialized with the promise of 54 Mbps or more effective bandwidth,making them a strong competitor to traditional wired Ethernet and themore ubiquitous “802.11b” or “WiFi” 11 Mbps mobile wireless transmissionstandard.

Generally speaking, transmission systems compliant with the IEEE 802.11aand 802.11g or “802.11a/g” as well as the 802.11n standards achievetheir high data transmission rates using Orthogonal Frequency DivisionModulation or OFDM encoded symbols mapped up to a 64 quadratureamplitude modulation (QAM) multi-carrier constellation. Generallyspeaking, the use of OFDM divides the overall system bandwidth into anumber of frequency sub-bands or channels, with each frequency sub-bandbeing associated with a respective sub-carrier upon which data may bemodulated. Thus, each frequency sub-band of the OFDM system may beviewed as an independent transmission channel within which to send data,thereby increasing the overall throughput or transmission rate of thecommunication system.

Generally, transmitters used in the wireless communication systems thatare compliant with the aforementioned 802.11a/802.11g/802.11n standardsas well as other standards such as the 802.16a/e/j/m IEEE Standard,perform multi-carrier OFDM symbol encoding (which may include errorcorrection encoding and interleaving), convert the encoded symbols intothe time domain using Inverse Fast Fourier Transform (IFFT) techniques,and perform digital to analog conversion and conventional radiofrequency (RF) upconversion on the signals. These transmitters thentransmit the modulated and upconverted signals after appropriate poweramplification to one or more receivers, resulting in a relativelyhigh-speed time domain signal with a large peak-to-average ratio (PAR).

Likewise, the receivers used in the wireless communication systems thatare compliant with the aforementioned 802.11a/802.11g/802.11n and802.16a/e/j/m IEEE standards generally include an RF receiving unit thatperforms RF downconversion and filtering of the received signals (whichmay be performed in one or more stages), and a baseband processor unitthat processes the OFDM encoded symbols bearing the data of interest.Generally, the digital form of each OFDM symbol presented in thefrequency domain is recovered after baseband downconversion,conventional analog to digital conversion and Fast FourierTransformation of the received time domain analog signal. Thereafter,the baseband processor performs frequency domain equalization (FEQ) anddemodulation to recover the transmitted symbols, and these symbols arethen processed in a viterbi decoder to estimate or determine the mostlikely identity of the transmitted symbol. The recovered and recognizedstream of symbols is then decoded, which may include deinterleaving anderror correction using any of a number of known error correctiontechniques, to produce a set of recovered signals corresponding to theoriginal signals transmitted by the transmitter.

Similarly, in a single carrier communication system, such as the IEEE802.11b standard, a transmitter performs symbol encoding (which mayinclude error correction encoding and interleaving), digital to analogconversion and conventional radio frequency (RF) upconversion on thesignals. These transmitters then transmit the modulated and upconvertedsignals after appropriate power amplification to one or more receivers.A receiver in a single carrier communication system includes an RFreceiving unit that performs RF downconversion and filtering of thereceived signals (which may be performed in one or more stages), and abaseband processor unit that demodulates and decodes (which may includedeinterleaving and error correction) the encoded symbols to produce aset of recovered signals corresponding to the original signalstransmitted by the transmitter.

In wireless communication systems, the RF modulated signals generated bythe transmitter may reach a particular receiver via a number ofdifferent propagation paths, the characteristics of which typicallychange over time due to the phenomena of multi-path and fading.Moreover, the characteristics of a propagation channel differ or varybased on the frequency of propagation. To compensate for the timevarying, frequency selective nature of the propagation effects, andgenerally to enhance effective encoding and modulation in a wirelesscommunication system, each receiver of the wireless communication systemmay periodically develop or collect channel state information (CSI) foreach of the frequency channels, such as the channels associated witheach of the OFDM sub-bands discussed above. Generally speaking, CSI isinformation defining or describing one or more characteristics abouteach of the OFDM channels (for example, the gain, the phase and the SNRof each channel). In a single carrier communication system, informationsimilar to CSI information may be developed by the receiver. Upondetermining the CSI for one or more channels, the receiver may send thisCSI back to the transmitter, which may use the CSI for each channel toprecondition the signals transmitted using that channel so as tocompensate for the varying propagation effects of each of the channels.

An important part of a wireless communication system is therefore theselection of the appropriate data rates, and the coding and modulationschemes to be used for a data transmission based on channel conditions.Generally speaking, it is desirable to use the selection process tomaximize throughput while meeting certain quality objectives, such asthose defined by a desired frame error rate (FER), latency criteria,etc.

To further increase the number of signals which may be propagated in thecommunication system and/or to compensate for deleterious effectsassociated with the various propagation paths, and to thereby improvetransmission performance, it is known to use multiple transmission andreceive antennas within a wireless transmission system. Such a system iscommonly referred to as a multiple-input, multiple-output (MIMO)wireless transmission system and is specifically provided for within the802.11n IEEE Standard now being adopted. Generally speaking, the use ofMIMO technology produces significant increases in spectral efficiencyand link reliability, and these benefits generally increase as thenumber of transmission and receive antennas within the MIMO systemincreases.

In addition to the frequency channels created by the use of OFDM, forexample, a MIMO channel formed by the various transmission and receiveantennas between a particular transmitter and a particular receiverincludes a number of independent spatial channels. As is known, awireless MIMO communication system can provide improved performance(e.g., increased transmission capacity) by utilizing the additionaldimensionalities created by these spatial channels for the transmissionof additional data. Of course, the spatial channels of a wideband MIMOsystem may experience different channel conditions (e.g., differentfading and multi-path effects) across the overall system bandwidth andmay therefore achieve different SNRs at different frequencies (i.e., atthe different OFDM frequency sub-bands) of the overall system bandwidth.Consequently, the number of information bits per modulation symbol(i.e., the data rate) that may be transmitted using the differentfrequency sub-bands of each spatial channel for a particular level ofperformance may differ from frequency sub-band to frequency sub-band.

However, instead of using the various different transmission and receiveantennas to form separate spatial channels on which additionalinformation is sent, better transmission and reception properties can beobtained in a MIMO system by using each of the various transmissionantennas of the MIMO system to transmit the same signal while phasing(and amplifying) this signal as it is provided to the varioustransmission antennas to achieve beamforming or beamsteering. Generallyspeaking, beamforming or beamsteering creates a spatial gain patternhaving one or more high gain lobes or beams (as compared to the gainobtained by an omni-directional antenna) in one or more particulardirections, while reducing the gain over that obtained by anomni-directional antenna in other directions. If the gain pattern isconfigured to produce a high gain lobe in the direction of each of thereceiver antennas, the MIMO system can obtain better transmissionreliability between a particular transmitter and a particular receiver,over that obtained by single transmitter-antenna/receiver-antennasystems.

There are many known techniques for determining a steering matrixspecifying the beamsteering coefficients that need to be used toproperly condition the signals being applied to the various transmissionantennas so as to produce the desired transmit gain pattern at thetransmitter. As is known, these coefficients may specify the gain andphasing of the signals to be provided to the transmitter antennas toproduce high gain lobes in particular or predetermined directions. Thesetechniques include, for example, transmit-MRC (maximum ratio combining)and singular value decomposition (SVD).

An important part of determining the steering matrix is taking intoaccount the specifics of the channel between the transmitter and thereceiver, referred to herein as the forward channel. As a result,steering matrixes are typically determined based on the CSI of theforward channel. To determine the CSI or other specifics of the forwardchannel, the transmitter must first send a known test or calibrationsignal to the receiver, which then computes or determines the specificsof the forward channel (e.g., the CSI for the forward channel) and thensends the CSI or other indications of the forward channel back to thetransmitter, thereby requiring signals to be sent both from thetransmitter to the receiver and then from the receiver back to thetransmitter in order to perform beamforming in the forward channel. Thisexchange typically occurs each time the forward channel is determined(e.g., each time a steering matrix is to be calculated for the forwardchannel).

Determining a steering matrix based on the CSI (or other information) ofthe forward channel is often referred to as explicit beamforming. Toreduce the amount of startup exchanges required to perform explicitbeamforming, it is known to perform implicit beamforming in a MIMOcommunication system. With implicit beamforming, the steering matrix iscalculated or determined based on the assumption that the forwardchannel (i.e., the channel from the transmitter to the receiver in whichbeamforming is to be accomplished) can be estimated from the reversechannel (i.e., the channel from the receiver to the transmitter). Inparticular, the forward channel can ideally be estimated as the matrixtranspose of the reverse channel. Thus, in the ideal case, thetransmitter only needs to receive signals from the receiver to produce asteering matrix for the forward channel, as the transmitter can use thesignals from the receiver to determine the reverse channel, and cansimply estimate the forward channel as a matrix transpose of the reversechannel. As a result, implicit beamforming reduces the amount of startupexchange signals that need to be sent between a transmitter and areceiver because the transmitter can estimate the forward channel basedsolely on signals sent from the receiver to the transmitter.Unfortunately, however, radio frequency (RF) chain impairments in theform of gain/phase imbalances and coupling losses impair the idealreciprocity between the forward and the reverse channels, making itnecessary to perform additional calibration exchanges each time theforward channel is being determined, to account for these impairments.

SUMMARY

In one embodiment, a method includes applying one or more beamsteeringmatrices to a plurality of signals to be transmitted via multipleantennas. The method also includes providing the plurality of signals toa plurality of power amplifiers coupled to the multiple antennas afterapplying the one or more beamsteering matrices to the plurality ofsignals. The method additionally includes determining signal energiesfor the plurality of signals provided to the plurality of poweramplifiers, and adjusting output power levels of the plurality of poweramplifiers based on the determined signal energies.

In another embodiment, a power amplifier control apparatus comprises acontroller that is configured to determine signal energies for aplurality of signals provided to a plurality of power amplifiers coupledto a plurality of transmit antennas, wherein one or more beamsteeringmatrices are applied to the plurality of signals. Additionally, thecontroller is configured to generate control signals to adjust outputpower levels of the plurality of power amplifiers based on thedetermined signal energies.

In yet another embodiment, a wireless transmitter for transmitting aninformation signal comprises a signal modulator adapted to modulate theinformation signal to produce a modulated signal. Also, the wirelesstransmitter comprises a plurality of transmission antennas, and abeamforming network coupled between the signal modulator and theplurality of transmission antennas. Additionally, the wirelesstransmitter comprises a first controller coupled to the beamformingnetwork to control the beamforming network using one or more steeringmatrices so as to produce a transmit gain pattern having one or morehigh gain lobes when the modulated signal is transmitted via theplurality of transmission antennas. The wireless transmitter furthercomprises a plurality of power amplifiers coupled to the beamformingnetwork and the plurality of transmission antennas, and a secondcontroller coupled to the plurality of amplifiers. The second controlleris configured to determine signal energies for a plurality of signalsprovided to the plurality of power amplifiers, and generate controlsignals to adjust output power levels of the plurality of poweramplifiers based on the determined signal energies.

In still another embodiment, a method of wirelessly transmitting aninformation signal via multiple antennas includes modulating theinformation signal to produce a modulated signal, and applying one ormore beamsteering matrices to the modulated signal to produce aplurality of output signals. The method additionally includes providingthe plurality of output signals to a plurality of power amplifiers,wherein the plurality of power amplifiers are coupled to the multipleantennas. The method also includes determining signal energies for theplurality of output signals, and adjusting output power levels of theplurality of power amplifiers based on the determined signal energies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless MIMO communication ortransmission system that implements transmit beamforming and than mayutilize power amplifier control techniques such as described herein;

FIG. 2 is a block diagram illustrating a transmit gain pattern forwireless communications between a single transmitter and a singlereceiver implemented using transmitter beamforming;

FIG. 3 is a block diagram illustrating a transmit gain pattern forwireless communications between a single transmitter and multiplereceivers implemented using transmitter beamforming;

FIG. 4 is a block diagram of an example power amplifier control systemthat may be included in the transmitter 12 of FIG. 1;

FIG. 5 is a flow diagram of an example method for power amplifiercontrol that may be implemented in a power amplifier control system suchas the example system of FIG. 4;

FIG. 6 is a flow diagram of another example method for power amplifiercontrol that may be implemented in a power amplifier control system suchas the example system of FIG. 4;

FIG. 7 is a flow diagram of another example method for power amplifiercontrol that may be implemented in a power amplifier control system suchas the example system of FIG. 4;

FIG. 8A is a block diagram of a high definition television that mayutilize power amplifier control techniques such as described herein;

FIG. 8B is a block diagram of a vehicle that may utilize power amplifiercontrol techniques such as described herein;

FIG. 8C is a block diagram of a cellular phone that may utilize poweramplifier control techniques such as described herein;

FIG. 8D is a block diagram of a set top box that may utilize poweramplifier control techniques such as described herein;

FIG. 8E is a block diagram of a media player that may utilize poweramplifier control techniques such as described herein; and

FIG. 8F is a block diagram of a voice over IP device that may utilizepower amplifier control techniques such as described herein.

DETAILED DESCRIPTION

While the power amplifier control techniques described herein foreffecting a wireless data transmission are described as being used incommunication systems that use one of the IEEE Standard 802.11xcommunication standards, techniques such as described herein may be usedin various other types of wireless communication systems and are notlimited to those conforming to one or more of the IEEE Standard 802.11xstandards. As just two examples, power amplifier control techniques suchas described herein may be used in systems that use one of the IEEEStandard 802.16x communication standards or in systems that use codedivision multiple access (CDMA) modulation.

Referring now to FIG. 1, a MIMO communication system 10 is illustratedin block diagram form as generally including a single transmitter 12having multiple transmission antennas 14A-14N and a single receiver 16having multiple receiver antennas 18A-18M. The number of transmissionantennas 14A-14N can be the same as, more than, or less than the numberof receiver antennas 18A-18M. As shown in FIG. 1, the transmitter 12 mayinclude a controller 20 coupled to a memory 21, a symbol encoder andmodulator unit 22 and a space-time filtering or mapping block 24, alsoreferred to herein as a transmit beamforming network. The transmitter 12may also include a matrix equalizer 25 and a symbol demodulator anddecoder unit 26 to perform demodulation and decoding of signals receivedvia the antennas 14A-14N in a receive mode. Additionally, thetransmitter 12 includes a steering matrix calculation unit 28. Thecontroller 12 may be any desired type of controller and both thecontroller 12 and the steering matrix calculation unit 28 may beimplemented as one or more standard multi-purpose, programmableprocessors, such as micro-processors, as application specific integratedcircuits (ASICs), etc., or may be implemented using any other desiredtypes of hardware, software and/or firmware. Likewise, the space-timemapping block 24 or beamforming network, and the matrix equalizer 25 maybe implemented using known or standard hardware and/or softwareelements. If desired, various of the transmitter components, such as thecontroller 20, the modulator unit 22, the demodulator unit 26, thesteering matrix calculation unit 28, the space-time mapping block 24 andthe matrix equalizer 25 may be implemented in the same or in differenthardware devices, such as in the same or different processors.Additionally, each of these components of the transmitter 12 may bedisposed in a housing 29 (shown in dotted relief in FIG. 1). Stillfurther, the routines or instructions for implementing the functionalityof any of these components may be stored in the memory 21 or withinother memory devices associated with the individual hardware used toimplement these components.

During operation, information signals T_(x1)-T_(xn) which are to betransmitted from the transmitter 12 to the receiver 16 are provided tothe symbol encoder and modulator unit 22 for encoding and modulation. Ofcourse, any desired number of signals T_(x1)-T_(xn) may be provided tothe modulator unit 22, with this number generally being limited by themodulation scheme used by and the bandwidth associated with the MIMOcommunication system 10. Additionally, the signals T_(x1)-T_(xn) may beany type of signals, including analog or digital signals, and mayrepresent any desired type of data or information. Additionally, ifdesired, a known test or control signal C_(x1) (which may be stored inthe memory 21) may be provided to the symbol encoder and modulator unit22 for use in determining CSI related information describing thecharacteristics of the channel(s) between the transmitter 12 and thereceiver 16. If desired, the same control signal or a different controlsignal may be used to determine the CSI for each frequency and/orspatial channel used in the MIMO communication system 10. The controlsignal C_(x1) may be a sounding packet, for example.

The symbol encoder and modulator unit 22 may interleave digitalrepresentations of the various signals T_(x1)-T_(xn) and C_(x1) and mayperform any other known type(s) of error-correction encoding on thesignals T_(x1)-T_(xn) and C_(x1) to produce one or more streams ofsymbols to be modulated and sent from the transmitter 12 to the receiver16. While the symbols may be modulated using any desired or suitable QAMtechnique, such as using 64 QAM, these symbols may be modulated in anyother known or desired manner including, for example, using any otherdesired phase and/or frequency modulation techniques. In any event, themodulated symbol streams are provided by the symbol encoder andmodulator unit 22 to the space-time mapping block 24 for processingbefore being transmitted via the antennas 14A-14N. While notspecifically shown in FIG. 1, the modulated symbol streams may beup-converted to the RF carrier frequencies associated with an OFDMtechnique (in one or more stages) before being processed by thespace-time mapping block 24 in accordance with a beamforming techniquemore specifically described herein. Upon receiving the modulatedsignals, the space-time mapping block 24 or beamforming networkprocesses the modulated signals by injecting delays and/or gains intothe modulated signals based on a steering matrix provided by thecontroller 20 and/or the steering matrix calculation block, to therebyperform beamsteering or beamforming via the transmission antennas14A-14N.

The signals transmitted by the transmitter 12 are detected by thereceiver antennas 18A-18M and may be processed by a matrix equalizer 35within the receiver 16 to enhance the reception capabilities of theantennas 18A-18M. As will be understood, the processing applied at thereceiver 16 (as well as at the transmitter 12) may be based on, forexample, the CSI developed by the receiver 16 in response to thetransmission of the test or control signal C_(x1) (e.g., a soundingpacket). In any event, a symbol demodulator and decoder unit 36, undercontrol of a controller 40, may decode and demodulate the receivedsymbol strings as processed by the matrix equalizer 35. In this process,these signals may be downconverted to baseband. Generally, the matrixequalizer 35 and the demodulator and decoder unit 36 may operate toremove effects of the channel based on the CSI as well as to performdemodulation on the received symbols to produce a digital bit stream. Insome cases, if desired, the symbol demodulator and decoder unit 36 mayperform error correction decoding and deinterleaving on the bit streamto produce the received signals R_(x1)-R_(xn) corresponding to theoriginally transmitted signals T_(x1)-T_(xn).

As shown in FIG. 1, the receiver 16 may also include a memory 41 and asymbol encoder and modulator unit 46 which may receive one or moresignals T_(R1)-T_(Rm) which may be encoded and modulated using anydesired encoding and modulation techniques. The encoded and modulatedsymbol stream may then be upconverted and processed by a space-timemapping block 34 to perform beamsteering based on a steering matrixdeveloped by a steering matrix calculation unit 48, prior to beingtransmitted via the receiver antennas 18A-18N to, for example, thetransmitter 12, thereby implementing the reverse link. As shown in FIG.1, each of the receiver components may be disposed in a housing 49.

The matrix equalizer 25 and the demodulator/decoder unit 26 within thetransmitter 12 operate similarly to the matrix equalizer 35 and thedemodulator/decoder unit 36 of the receiver 16 to demodulate and decodethe signals transmitted by the receiver 16 to produce the recoveredsignals R_(R1)-R_(Rm). Here again, the matrix equalizer 25 may processthe received signals in any known manner to enhance the separation andtherefore the reception of the various signals transmitted by theantennas 18A-18M. Of course, the CSI for the various OFDM channel(s) maybe used by the steering matrix calculation units 28 and 48 as well as bythe controllers 20 and 40 to perform beamforming and to determine asteering matrix used by the space-time mapping blocks 24, 34. As notedabove, the CSI, beamforming and other programs and data such as thesteering matrix used by the units 28 and 48 and by the controllers 20and 40 may be stored in the memories 21 and 41.

As is generally known, beamforming or beamsteering typically includesapplying appropriate phases and gains to the various signals as sentthrough the multiple transmitter antennas 14A-14N, in a manner withcauses the signals sent from the different transmitter antennas 14A-14Nto constructively interact (add in phase) in certain predetermineddirections and to deconstructively interact (cancel) in otherdirections. Thus, beamsteering typically produces a beam pattern havinghigh gain regions (referred to as high gain lobes) in variouspredetermined directions and low gain regions (typically referred to asnulls) in other directions. The use of beamforming techniques in a MIMOsystem enables a signal to be sent with high gain (as compared to anomni-directional antenna) in certain directions, and to be sent with lowgain (as compared to an omni-directional antenna) in other directions.Thus, in the MIMO system 10 of FIG. 1, beamforming may be used toenhance signal directivity towards the receiver antennas 18A-18M, whichimproves the SNR of the transmissions and results in more reliabletransmissions. In this case, the beamforming technique will generallyform high gain lobes in the direction of propagation at which thehighest gain is desired, and in particular in the directions ofpropagation from the transmitter 12 to each of the receiver antennas18A-18M of the receiver 16.

To implement beamforming in the transmitter 12, the steering matrixcalculation unit 28 may determine or calculate a set of matrixcoefficients (referred to herein as a steering matrix) which are used bythe space-time mapping block or beamforming network 24 to condition thesignals being transmitted by the antennas 14A-14N. If desired, thesteering matrix for any particular frequency channel of the MIMO system10 may be determined by the steering matrix calculation unit 28 based onthe CSI determined for that channel (wherein the CSI is usuallydeveloped by and sent from the receiver 16 but may instead be developedfrom signals sent from the receiver 16 to the transmitter 12 in thereverse link as an estimate of the forward link).

To illustrate beamforming, FIG. 2 shows a MIMO communication system 110having a single transmitter 112 with six transmission antennas114A-114F, and a single receiver 116 with four receiver antennas118A-118D. In this example, the steering matrix may be developed by thetransmitter 112 or the receiver 116, using explicit beamforming orimplicit beamforming methods. As illustrated in FIG. 2, the transmitgain pattern 119 includes multiple high gain lobes 1119A-119D disposedin the directions of the receiver antennas 118A-118D. The high gainlobes 1119A-119D are orientated in the directions of propagation fromthe transmitter 112 to the particular receiver antennas 118A-118D whilelower gain regions, which may even include one or more nulls, areproduced in other directions of propagation. While FIG. 2 illustrates aseparate high gain lobe directed to each of the receiver antennas118A-118D, it will be understood that the actual gain pattern producedby the beam steering matrix calculations may not necessarily include aseparate high gain lobe for each of the receiver antennas 118A-118D.Instead, the gain pattern produced by the beam steering matrixcalculations for the transmitter 112 may have a single high gain lobecovering or directed generally to more than one of the receiver antennas118A-118D. Thus, it is to be understood that the beam pattern resultingfrom the creation of a steering matrix may or may not have separate highgain lobes separated by low gain regions or nulls for each of thereceiver antennas.

Of course, developing the beam pattern 119 to have high gain regions andlow gain regions may be performed in any desired manner and location.For example, any of the components within the transmitter 12 or withinthe receiver 16 of FIG. 1, including the controllers 20, 40 and thesteering matrix calculation units 28, 48 may generate and/or process thesteering information. For example, the controller 20 or the steeringmatrix calculation unit 28 within the transmitter 12 may determine thesteering matrix for use in the space-time mapping block 24 forperforming beamforming to the receiver 16. On the other hand, thecontroller 40 or the steering matrix calculation unit 48 within thereceiver 16 may determine the steering matrix for use in the space-timemapping block 24 of the transmitter 12, and may then transmit thissteering matrix to the transmitter 12.

The receiver 116 may compute the steering matrix to be used by thetransmitter 112 based on the CSI developed by the receiver 116, and maysend the actual steering matrix to the transmitter 112 to be used intransmitting information to the receiver 16. On the other hand, thesteering matrix for the transmitter space-time mapping block 24 of FIG.1 may be calculated by the steering matrix calculation unit 28 withinthe transmitter 12 based on the CSI provided and sent back from thereceiver 16 to the transmitter 12. As another alternative, the steeringmatrix for the transmitter space-time mapping block 24 of FIG. 1 may becalculated by the steering matrix calculation unit 28 within thetransmitter 12 based on the CSI associated with the reverse channel(i.e., from the receiver 16 to the transmitter 12).

Of course, the techniques described herein are not limited to being usedin a transmitter of a MIMO communication system communicating with asingle receiver of the MIMO communication system, but can additionallybe applied when a transmitter of a MIMO communication system iscommunicating with multiple receivers, each of which has one or morereceiver antennas associated therewith. For example, FIG. 3 illustratesa MIMO system 210 in which a single transmitter 212 having multiple (inthis example six) transmission antennas 214A-214F transmits to multiplereceivers 216, 218, 220 and 222, each having multiple receiver antennas226A-226C, 228A-228C, 230A-230D, and 232A-232D, respectively. Whileshown in this example as including three or four receiver antennas, anyor all of the receivers 216, 218, 220, 222 of FIG. 3 could includedifferent numbers of receiver antennas, including only a single receiverantenna if so desired. In any event, as illustrated by the transmit gainpattern 240 illustrated in FIG. 3, the steering matrix calculated andused by the transmitter 212 may be formed using CSI generated by one ormore of the receivers 216, 218, 220 and 222 and/or using CSI generatedbased on one or more reverse channels between the transmitter 212 andthe receivers 216, 218, 220 and 222.

In one example, the transmitter steering matrix may be calculated ordetermined using steering information generated by each of the receivers216, 218, 220 and 222, so that, as shown by the transmit gain pattern240, a high gain lobe is directed to at least one receiver antenna ofeach of the receivers 216, 218, 220, 222 at the same time. However, thesteering matrix need not necessarily produce a high gain lobe directedto all of the receiver antennas of each of the receivers 216, 218, 220,222, and not necessarily to all of the receiver antennas for anyparticular one of the receivers 216, 218, 220, 222. Thus, as illustratedin FIG. 3, the steering matrix for the transmitter 212 is determined insuch a manner that a separate high gain lobe is directed to each of thereceiver antennas 226A, 226B, 226C, 228A, 228C, 230A, 230B and 230D.However, due to the physical location of the receiver 222 and itsantennas with respect to the transmitter 212, a single high gain lobe isdirected to the receiver antennas 232A-232D, resulting in a single highgain lobe in the transmit gain pattern 240 directed to all of thesereceiver antennas.

In another example, the transmitter steering matrix may be calculated ordetermined using CSI information associated with reverse channelsbetween the transmitter 212 and each of the receivers 216, 218, 220 and222.

On the other hand, the transmitter 212 may develop a different steeringmatrix for each of the receivers 216, 218, 220 and 222 using steeringinformation generated by the different receivers, and may use thosesteering matrices to beamform to the separate or different receivers atdifferent times or using different channels, e.g., OFDM channels, of thesystem. As another example, the transmitter 212 may develop a differentsteering matrix for each of the receivers 216, 218, 220 and 222 usingCSI information associated with reverse channels between the transmitter212 and each of the receivers 216, 218, 220 and 222.

While, in many cases, it will be desirable to beamform in such a way todirect a high gain lobe to at least one receiver antenna from eachreceiver, it may not be necessary to implement this requirement in allcases. For example, a particular receiver may be in a direct line ofsight from the transmitter to another receiver and therefore may bedisposed in a high gain region of the transmitter and may thusadequately receive the transmitted signals from the transmitter withoututilizing steering information generated by that receiver. As anotherexample, a particular receiver may be disposed in a low gain regionassociated with the transmitter, but may be disposed relatively close tothe transmitter so that the particular receiver adequately receives thesignals transmitted by the transmitter without utilizing steeringinformation generated by that receiver. Of course, if desired, thenumber and location (identity) of the receivers used in calculating thetransmitter steering matrix can be determined in any manner, includingby trial and error, in determining an acceptable or optimal steeringmatrix using steering information generated by more than one receiver.Still further, while the maximum gains of the high gain lobes of each ofthe transmit gain patterns shown in FIGS. 2 and 3 are shown as being thesame, the steering matrix calculation units 28 and 48 may developsteering matrixes which produce high gain lobes with differing maximumgains.

Referring again to FIG. 1, the space-time mapping block 24 orbeamforming network processes applies the steering matrix to themodulated signals to thereby perform beamsteering or beamforming via thetransmission antennas 14A-14N. In a MIMO system, a beamformed or steeredsignal that is received by a receiver may be represented as:

y=HQ _(steer) s+n  (Equation 1)

where:y is an N_(Rx)×1 received signal vector;N_(Rx) is a number of receive antennas;n is an N_(Rx)×1 additive noise vector;s an N_(SS)×1 transmitted signal vector;N_(SS) is a number of spatial streams;H is an N_(Rx)×N_(Tx) matrix indicative of a MIMO channel;N_(Tx) is a number of transmit antennas; andQ_(steer) is an N_(Tx)×N_(SS) steering matrix.

In communication systems that utilize OFDM, Equation 1 may correspond toeach subcarrier or to each of a plurality of groups of subcarriers. Forexample, in a MIMO-OFDM system, a beamformed or steered signal that isreceived by a receiver may be represented as:

y _(k) =H _(k) Q _(steer,k) s _(k) +n _(k)  (Equation 2)

where:y_(k) is an N_(Rx)×1 received signal vector for a k^(th) subcarrier or ak^(th) group of subcarriers;n_(k) is an N_(Rx)×1 additive noise vector for the k^(th) subcarrier ork^(th) group of subcarriers;s_(k) is an N_(SS)×1 transmitted signal vector for the k^(th) subcarrieror k^(th) group of subcarriers;H_(k) is an N_(Rx)×N_(Tx) matrix indicative of a MIMO channel for thek^(th) subcarrier or k^(th) group of subcarriers; andQ_(steer,k) is an N_(Tx)×N_(SS) spatial steering matrix for the k^(th)subcarrier or k^(th) group of subcarriers.

After the steering matrix has been applied to the modulated signals, thesignals may be provided to a plurality of power amplifiers (PAs), eachPA corresponding to a different one of the antennas 14. In a typicalMIMO transmitter, each PA is driven at a maximum output power level. Themaximum output power level may be a level at which output power ismaximized and distortion remains at or below a defined, acceptable levelor one or more other performance criteria are met.

FIG. 4 is a block diagram of an example power amplifier system 300 thatmay be utilized in a transmitter such as the transmitter 12 of FIG. 1.Generally, the power amplifier system 300 controls the output power ofPAs based on the energy of signals that are provided as inputs to thePAs. For ease of explanation, the system 300 will be described withreference to FIG. 1. Of course, the example power amplifier system 300can be utilized in transmitters other than the transmitter 12.Additionally, the transmitter 12 may utilize power amplifier systemsother than the system 300.

In the example of FIG. 4, the system 300 includes three power amplifiers304, 308, and 312, corresponding to three antennas 14A, 14B and 14C. Inembodiments with different numbers of antennas (e.g., 2, 4, 5, 6, 7,etc.), the system may include a corresponding different number of poweramplifiers. A controller 316 is coupled to the power amplifiers 304,308, and 312, and generates power control signals that are provided tothe power amplifiers 304, 308, and 312 to control the output power ofeach of the power amplifiers 304, 308, and 312. The power controlsignals control the power level of each of the power amplifiers 304,308, and 312. The controller 316 may be included in the controller 20,the space-time mapping block 24, or any other component of thetransmitter 12 illustrated in FIG. 1. Alternatively, the controller 316may be a controller that is separate from the components of thetransmitter 12 illustrated in FIG. 1. Additionally, the controller 316may be a distributed controller that is distributed amongst one or more(or none)

The power amplifiers 304, 308, 312, receive outputs of the space-timemapping block (i.e., modulated signals to which the steering matrix hasbeen applied) and amplify these signals for transmission via theantennas 14A, 14B and 14C. The controller 316 also may receive theoutputs of the space-time mapping block. As will be described in moredetail below, the controller 316 may generate the power control signalsoptionally based on the outputs of the space-time mapping block (i.e.,the inputs to the PAs 304, 308 and 312).

The controller 316 optionally may be coupled to a steering matrix memory320 that has stored therein the steering matrix that is applied by thespace-time mapping block 24. The memory 320 may be included in thesteering matrix calculator 28, the controller 20, the space-time mappingblock 24, or any other component of the transmitter 12 illustrated inFIG. 1. Alternatively, the memory 320 may be separate from thecomponents of the transmitter 12 illustrated in FIG. 1. As will bedescribed in more detail below, the controller 316 may generate thepower control signals optionally based on the steering matrix that isapplied by the space-time mapping block 24.

FIG. 5 is a flow diagram of an example method 350 for adjusting outputpower of PAs based on the energy of signals that are provided as inputsto the PAs. The method 350 may be implemented by the PA system 300 ofFIG. 4 and will be described with reference to FIG. 4 for ease ofexplanation. Of course, the method 350 may be implemented by a systemother than the system 300 of FIG. 4. Similarly, the system 300 mayimplement a method different than that of FIG. 5.

At a block 354, signal energies at the inputs to the PAs may bedetermined. In one embodiment, the actual signals provided to the PAsmay be evaluated to determine the energy levels. The energy level of asignal provided to a PA may be calculated any of a variety of suitabletechniques. As just one example, the energy level of a signal could bebased on calculating an average squared amplitude of the signal.Referring to FIG. 4, if the controller 316 is coupled to the inputs ofthe PAs 304, 308, 312, the controller 316 may calculate the energylevels of the signals provided to the PAs 304, 308, 312.

In another embodiment, the energy levels of the signals provided to thePAs may be estimated by evaluating the steering matrix or matrices. Eachrow of the steering matrix may correspond to a different one of theantennas. Generally, the “energy” of a row of a steering matrix isproportional to the energy of the corresponding signal after thesteering matrix has been applied to the signal. Thus, the energy of theinput to a PA can be estimated based on the “energy” of a row of thesteering matrix. For example, the energy of the input to a PA can beestimated based on a sum of squared magnitudes of coefficients in a rowof a steering matrix.

In an OFDM system, there may be multiple steering matrices correspondingto each subcarrier or to each of a plurality of groups of subcarriers.In such systems, the energy of the input to a PA can be estimated basedon each corresponding row of the multiple steering matrices. Forexample, a sum of squared magnitudes of coefficients in eachcorresponding row of the multiple steering matrices may be calculated.In another embodiment, the energy of the input to a PA can be estimatedbased on each corresponding row of a subset of the multiple steeringmatrices. For instance, steering matrices corresponding to less than allof the subcarriers or groups of subcarriers may be analyzed. Forexample, a subset of steering matrices may be selected, and a sum ofsquared magnitudes of coefficients in each corresponding row of theselected steering matrices may be calculated.

Referring to FIG. 4, if the controller 316 receives the steering matrixor matrices, the controller 316 may calculate the energy levels of thesignals provided to the PAs 304, 308, 312 based on the steering matrixor matrices.

At a block 358, the signal energies determined at the block 354 may becompared. In one embodiment, comparing the signal energies may includedetermining a maximum signal energy, and then comparing each othersignal energy to the maximum signal energy. In this embodiment,comparing each other signal energy to the maximum signal energy mayinclude calculating a ratio for each other signal energy to the maximumsignal energy. For example, if there are three antennas, the signalenergies may be designated as E₁, E₂ and E₃. Assuming that it isdetermined that the maximum signal energy is E₁, then a ratio α₁ may becalculated as E₁/E₂, and a ratio α₂ may be calculated as E₁/E₃.Referring to FIG. 4, the controller 316 compares the signal energies.

At a block 362, output powers of the PAs may be adjusted based on thecomparisons determined at the block 358. Generally, adjusting the outputpowers of the PAs may include adjusting the output powers to reflectrelative energy levels of the signals provided to the PAs. For instance,the output powers of the PAs may be adjusted so that the relative outputpowers generally correspond to the relative energy levels of the signalsprovided to the PAs. For example, in an embodiment in which a ratio orratios are calculated between a maximum input signal energy level andone or more other signal energy levels, the output powers of the PAs maybe adjusted so that a ratio or ratios between the output power level ofthe PA corresponding to the maximum input signal energy level and theother output power level(s) correspond to the ratio or ratios of theinput signal energy levels. For instance, the PA corresponding to themaximum input signal energy level may be set to a defined output powerlevel, such as a maximum output power level. The output power levels ofthe remaining PA(s) may be controlled so that the ratio(s) between thedefined output power level and the power levels of the remaining PAscorrespond to the ratio(s) between the maximum input signal energy leveland the input signal energy level(s) of the remaining PA(s).

Referring to FIG. 4, the controller 316 may adjust the output power ofeach of the PAs 304, 308, 312 by generating control signals that controlthe output power of each of the PAs 304, 308, 312. The controller 316may adjust the output power of each of the PAs 304, 308, 312 so that therelative output powers of the PAs 304, 308, 312 correspond to therelative energy levels of the signals provided to the PAs 304, 308, 312.

FIG. 6 is a flow diagram of an example method 400 that corresponds toone specific implementation of the method 350 of FIG. 5. It will beunderstood, however, that the method 350 may be implemented in manyother ways as well. The method 400 may be implemented by the PA system300 of FIG. 4 and will be described with reference to FIG. 4 for ease ofexplanation. Of course, the method 400 may be implemented by a systemother than the system 300 of FIG. 4. Similarly, the system 300 mayimplement a method different than the method 400.

At a block 404, signal energies at the inputs to the PAs may bedetermined. The input signal energies may be determined as describedabove with respect to the block 354 of FIG. 5, for example. Referring toFIG. 4, if the controller 316 is coupled to the inputs of the PAs 304,308, 312, the controller 316 may calculate the energy levels of thesignals provided to the PAs 304, 308, 312. Additionally oralternatively, if the controller 316 receives the steering matrix ormatrices, the controller 316 may calculate the energy levels of thesignals provided to the PAs 304, 308, 312 based on the steering matrixor matrices.

At a block 408, a maximum of the input signal energies calculated at theblock 404 may be determined. The maximum signal energy may be denoted asE_(max). Referring to FIG. 4, the controller 316 may determine themaximum of the input signal energies.

At a block 412, one or more ratios may be determined for the one or moreremaining signal energy levels. For example, if there are threeantennas, the signal energies may be designated as E₁, E₂ and E₃.Assuming that it is determined that the E_(max)=E₁, then a ratio α₁ maybe calculated as E₁/E₂, and a ratio α₂ may be calculated as E₁/E₃.Referring to FIG. 4, the controller 316 calculates the one or moreratios.

At a block 416, an output power level of the PA corresponding to E_(max)may be set to a defined level. For example, the output power level ofthe PA corresponding to E_(max) may be set to the maximum output powerlevel. The maximum level may be adjustable and/or reconfigurable. Asanother example, the output power of the PA corresponding to E_(max) maybe set to a defined level that is less than the maximum level. Referringto FIG. 4, the controller 316 may set the output power of the PAcorresponding to E_(max) to the defined level by generating a controlsignal that is provided to the PA corresponding to E_(max).

At a block 420, the output power of the one or more remaining PAs may beset below the defined level based on the ratios determined at the block412. Continuing with the three-antenna example discussed above, ifE_(max)=E₁, ratios α₁ and α₂ have been calculated, and assuming theoutput power level for the PA corresponding to E₁ has been set to adefined level P_(max), the output power level of the PA corresponding E₂can be set to P_(max)/α₁, and the output power level of the of the PAcorresponding E₃ can be set to P_(max)/α₂ Referring to FIG. 4, thecontroller 316 may set the output power of the PA corresponding E₂ toP_(max)/α₁, and may set the power level of the of the PA correspondingE₃ to P_(max)/α₂ by generating control signals that are provided to thePAs corresponding to E₂ and E₃.

FIG. 7 is a flow diagram of another example method 450 for adjustingoutput power of PAs based on the energy of signals that are provided asinputs to the PAs. The method 450 may be implemented by the PA system300 of FIG. 4 and will be described with reference to FIG. 4 for ease ofexplanation. Of course, the method 450 may be implemented by a systemother than the system 300 of FIG. 4. Similarly, the system 300 mayimplement a method different than the method 450.

At a block 454, signal energies at the inputs to the PAs may bedetermined. The input signal energies may be determined as describedabove with respect to the block 354 of FIG. 5, for example. Referring toFIG. 4, if the controller 316 is coupled to the inputs of the PAs 304,308, 312, the controller 316 may calculate the energy levels of thesignals provided to the PAs 304, 308, 312. Additionally oralternatively, if the controller 316 receives the steering matrix ormatrices, the controller 316 may calculate the energy levels of thesignals provided to the PAs 304, 308, 312 based on the steering matrixor matrices.

At a block 458, output powers of the PAs may be adjusted based on theenergy levels determined at the block 454 so that the output powers ofthe PAs are approximately the same level. In one embodiment, adjustingthe output powers of the PAs may include adjusting the output powersbased on relative energy levels of the signals provided to the PAs. Forinstance, similar to the block 408 of FIG. 6, a maximum of the inputsignal energies calculated at the block 454 may be determined (denotedas E_(max)). Then, similar to the block 412 of FIG. 6, one or moreratios may be determined for the one or more remaining signal energylevels. For example, if there are three antennas, the signal energiesmay be designated as E₁, E₂ and E₃. Assuming that it is determined thatthe E_(max)=E₁, then a ratio α₁ may be calculated as E₁/E₂, and a ratioα₂ may be calculated as E_(max)/E₃. Next, similar to the block 416 ofFIG. 6, an output power level of the PA corresponding to E_(max) may beset to a defined level. For example, the output power level of the PAcorresponding to E_(max) may be set to the maximum output power level.The maximum level may be adjustable and/or reconfigurable. As anotherexample, the output power of the PA corresponding to E_(max) may be setto a defined level that is less than the maximum level. Then, the outputpower of the one or more remaining PAs may be set based on thedetermined ratios so that the output powers of the remaining PAs arealso at the defined level. Continuing with the three-antenna examplediscussed above, if E_(max)=E₁, ratios α₁ and α₂ have been calculated,and assuming the output power level for the PA corresponding to E₁ hasbeen set to a defined level P_(max), the output power level of the PAcorresponding E₂ can be set to P_(max)·α₁, and the output power level ofthe of the PA corresponding E₃ can be set to P_(max)·α₂ Referring toFIG. 4, the controller 316 may set the output power of the PAcorresponding E₂ to P_(max)·α₁, and may set the power level of the ofthe PA corresponding E₃ to P_(max)·α₂ by generating control signals thatare provided to the PAs corresponding to E₂ and E₃.

In another embodiment, adjusting the output powers of the PAs mayinclude adjusting the output powers based on energy levels of thesignals provided to the PAs compared to a reference energy level. Forinstance, each of the input signal energies may be compared to areference energy level E_(REF). Then, multiple ratios may be determinedcorresponding to the signal energy levels determined at the block 454compared to E_(REF). For example, if there are three antennas, thesignal energies may be designated as E₁, E₂ and E₃. Then, a ratio α₁ maybe calculated as E₁/E_(REF); a ratio α₁ may be calculated as E₂/E_(REF);and a ratio α₂ may be calculated as E₃/E_(REF). Next, the output powersof the PAs may be set based on the determined ratios so that the outputpowers of the remaining PAs are approximately equal. Referring to FIG.4, the controller 316 may set the output power of the PAs based on thedetermined ratios by generating control signals that are provided to thePAs 304, 308, 312.

Of course, the output powers of the PAs may be adjusted based on theenergy levels determined at the block 454 in other ways as well, so thatthe output powers of the PAs are approximately the same level.

In some embodiments, PA output level adjustment may be disabled. Forexample, it may be determined in some situations that the output levelsof all of the PAs should be kept at or near the same level, such as themaximum output power level. For instance, if the rows of the steeringmatrix have nearly the same energy, and/or if (in an OFDM system) if theenergy level of each signal varies significantly between thesubchannels, it may be determined that the output levels of all of thePAs should be kept at or near the same level.

Although examples were described above in which a transmitter includedthree antennas, it will be apparent to one of ordinary skill in the artthat power amplifier control techniques such as described herein can beapplied to transmitters having different numbers of antennas such astwo, four, five, six, seven, etc.

The power amplifier control techniques described above may be utilizedin various MIMO devices. For example, power amplifier control techniquessuch as described above may be utilized in base stations, access points,wireless routers, personal computers, mobile communication devices,mobile phones, etc. Additionally, FIGS. 8A-8F illustrate various devicesin which power amplifier control techniques such as described above, maybe employed.

Referring now to FIG. 8A, such techniques may be utilized in a highdefinition television (HDTV) 1020. HDTV 1020 includes a mass datastorage 1027, an HDTV signal processing and control block 1022, a WLANinterface and memory 1028. HDTV 1020 receives HDTV input signals ineither a wired or wireless format and generates HDTV output signals fora display 1026. In some implementations, signal processing circuitand/or control circuit 1022 and/or other circuits (not shown) of HDTV1020 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other type of HDTVprocessing that may be required.

HDTV 1020 may communicate with a mass data storage 1027 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.The mass storage device may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″HDTV1020 may be connected to memory 1028 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. HDTV 1020 also may support connections with a WLAN via aWLAN network interface 1029. The WLAN network interface 1029 mayimplement power amplifier control techniques and/or include a poweramplifier control system such as described above.

Referring now to FIG. 8B, such techniques may be utilized in a vehicle1030. The vehicle 1030 includes a control system that may include massdata storage 1046, as well as a WLAN interface 1048. The mass datastorage 1046 may support a powertrain control system 1032 that receivesinputs from one or more sensors 1036 such as temperature sensors,pressure sensors, rotational sensors, airflow sensors and/or any othersuitable sensors and/or that generates one or more output controlsignals 1038 such as engine operating parameters, transmission operatingparameters, and/or other control signals.

Control system 1040 may likewise receive signals from input sensors 1042and/or output control signals to one or more output devices 1044. Insome implementations, control system 1040 may be part of an anti-lockbraking system (ABS), a navigation system, a telematics system, avehicle telematics system, a lane departure system, an adaptive cruisecontrol system, a vehicle entertainment system such as a stereo, DVD,compact disc and the like.

Powertrain control system 1032 may communicate with mass data storage1027 that stores data in a nonvolatile manner such as optical and/ormagnetic storage devices. The mass storage device 1046 may be a mini HDDthat includes one or more platters having a diameter that is smallerthan approximately 1.8″Powertrain control system 1032 may be connectedto memory 1047 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. Powertraincontrol system 1032 also may support connections with a WLAN via a WLANnetwork interface 1048. The control system 1040 may also include massdata storage, memory and/or a WLAN interface (all not shown). In oneexemplary embodiment, the WLAN network interface 1048 may implementpower amplifier control techniques and/or include a power amplifiercontrol system such as described above.

Referring now to FIG. 8C, such techniques may be used in a cellularphone 1050 that may include a cellular antenna 1051. The cellular phone1050 may include either or both signal processing and/or controlcircuits, which are generally identified in FIG. 8C at 1052, a WLANnetwork interface 1068 and/or mass data storage 1064 of the cellularphone 1050. In some implementations, cellular phone 1050 includes amicrophone 1056, an audio output 1058 such as a speaker and/or audiooutput jack, a display 1060 and/or an input device 1062 such as akeypad, pointing device, voice actuation and/or other input device.Signal processing and/or control circuits 1052 and/or other circuits(not shown) in cellular phone 1050 may process data, perform codingand/or encryption, perform calculations, format data and/or performother cellular phone functions.

Cellular phone 1050 may communicate with mass data storage 1064 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. The HDDmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″Cellular phone 1050 may beconnected to memory 1066 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. Cellular phone 1050 also may support connections with a WLANvia a WLAN network interface 1068. The WLAN network interface 1068 mayimplement power amplifier control techniques and/or include a poweramplifier control system techniques such as described above.

Referring now to FIG. 8D, such techniques may be utilized in a set topbox 1080. The set top box 1080 may include either or both signalprocessing and/or control circuits, which are generally identified inFIG. 8D at 1084, a WLAN interface and/or mass data storage 1090 of theset top box 1080. Set top box 1080 receives signals from a source suchas a broadband source and outputs standard and/or high definitionaudio/video signals suitable for a display 1088 such as a televisionand/or monitor and/or other video and/or audio output devices. Signalprocessing and/or control circuits 1084 and/or other circuits (notshown) of the set top box 1080 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any otherset top box function.

Set top box 1080 may communicate with mass data storage 1090 that storesdata in a nonvolatile manner and may use jitter measurement. Mass datastorage 1090 may include optical and/or magnetic storage devices forexample hard disk drives HDD and/or DVDs. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″Set top box 1080 may be connected to memory 1094 suchas RAM, ROM, low latency nonvolatile memory such as flash memory and/orother suitable electronic data storage. Set top box 1080 also maysupport connections with a WLAN via a WLAN network interface 1096. TheWLAN network interface 1096 may implement power amplifier controltechniques and/or include a power amplifier control system such asdescribed above.

Referring now to FIG. 8E, such techniques may be used in a media player1100. The media player 1100 may include either or both signal processingand/or control circuits, which are generally identified in FIG. 8E at1104, a WLAN interface and/or mass data storage 1110 of the media player1100. In some implementations, media player 1100 includes a display 1107and/or a user input 1108 such as a keypad, touchpad and the like. Insome implementations, media player 1100 may employ a graphical userinterface (GUI) that typically employs menus, drop down menus, iconsand/or a point-and-click interface via display 1107 and/or user input1108. Media player 1100 further includes an audio output 1109 such as aspeaker and/or audio output jack. Signal processing and/or controlcircuits 1104 and/or other circuits (not shown) of media player 1100 mayprocess data, perform coding and/or encryption, perform calculations,format data and/or perform any other media player function.

Media player 1100 may communicate with mass data storage 1110 thatstores data such as compressed audio and/or video content in anonvolatile manner and may utilize jitter measurement. In someimplementations, the compressed audio files include files that arecompliant with MP3 format or other suitable compressed audio and/orvideo formats. The mass data storage may include optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. The HDDmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″Media player 1100 may beconnected to memory 1114 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. Media player 1100 also may support connections with a WLAN viaa WLAN network interface 1116. The WLAN network interface 1116 mayimplement power amplifier control techniques and/or include a poweramplifier control system such as described above.

Referring to FIG. 8F, such techniques may be utilized in a Voice overInternet Protocol (VoIP) phone 1150 that may include an antenna 1152.The VoIP phone 1150 may include either or both signal processing and/orcontrol circuits, which are generally identified in FIG. 8F at 1154, awireless interface and/or mass data storage of the VoIP phone 1150. Insome implementations, VoIP phone 1150 includes, in part, a microphone1158, an audio output 1160 such as a speaker and/or audio output jack, adisplay monitor 1162, an input device 1164 such as a keypad, pointingdevice, voice actuation and/or other input devices, and a WirelessFidelity (WiFi) communication module 1166. Signal processing and/orcontrol circuits 1154 and/or other circuits (not shown) in VoIP phone1150 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other VoIP phone functions.

VoIP phone 1150 may communicate with mass data storage 1156 that storesdata in a nonvolatile manner such as optical and/or magnetic storagedevices, for example hard disk drives HDD and/or DVDs. The HDD may be amini HDD that includes one or more platters having a diameter that issmaller than approximately 1.8″VoIP phone 1150 may be connected tomemory 1157, which may be a RAM, ROM, low latency nonvolatile memorysuch as flash memory and/or other suitable electronic data storage. VoIPphone 1150 is configured to establish communications link with a VoIPnetwork (not shown) via WiFi communication module 1166. The WiFicommunication module 1166 may implement power amplifier controltechniques and/or include a power amplifier control system such asdescribed above.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented in hardware, firmware, software, orany combination of hardware, firmware, and/or software. For instance,the controller 316 may be implemented in hardware, firmware, software,or some combination of the hardware, firmware, and/or software. Forexample, the controller 316 may include hardware configured to implementall of the blocks of the method 350 of FIG. 5 and/or the method 400 ofFIG. 6. As another example, the controller 316 may comprise a processorcoupled to a memory that has stored therein computer readableinstructions that cause the processor to implement all of the blocks ofthe method 350 of FIG. 5 and/or the method 400 of FIG. 6. As yet anotherexample, the controller 316 may include hardware configured to implementsome of the blocks of the method 350 of FIG. 5 and/or the method 400 ofFIG. 6, and may include a processor coupled to a memory that has storedtherein computer readable instructions that cause the processor toimplement the other blocks of the method 350 of FIG. 5 and/or the method400 of FIG. 6. For instance, the block 354 and/or the block 404 may beimplemented in hardware, whereas the other blocks of the method 350 ofFIG. 5 and/or the method 400 of FIG. 6 may be implemented in software.

When implemented in software or firmware, the software or firmware maybe stored in any computer readable memory such as on a magnetic disk, anoptical disk, or other storage medium, in a RAM or ROM or flash memory,processor, hard disk drive, optical disk drive, tape drive, etc.Likewise, the software or firmware may be delivered to a user or asystem via any known or desired delivery method including, for example,on a computer readable disk or other transportable computer storagemechanism or via communication media. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism. The term “modulated data signal” means asignal that has one or more of its characteristics set or changed insuch a manner as to encode information in the signal. By way of example,and not limitation, communication media includes wired media such as awired network or direct-wired connection, and wireless media such asacoustic, radio frequency, infrared and other wireless media. Thus, thesoftware or firmware may be delivered to a user or a system via acommunication channel such as a telephone line, a DSL line, a cabletelevision line, a fiber optics line, a wireless communication channel,the Internet, etc. (which are viewed as being the same as orinterchangeable with providing such software via a transportable storagemedium). The software or firmware may include machine readableinstructions that are capable of causing one or more processors toperform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, it will be apparent to those of ordinaryskill in the art that changes, additions or deletions in addition tothose explicitly described above may be made to the disclosedembodiments without departing from the spirit and scope of theinvention.

1. A method, comprising: applying one or more beamsteering matrices to aplurality of signals to be transmitted via multiple antennas; afterapplying the one or more beamsteering matrices to the plurality ofsignals, providing the plurality of signals to a plurality of poweramplifiers coupled to the multiple antennas; determining signal energiesfor the plurality of signals provided to the plurality of poweramplifiers; and adjusting output power levels of the plurality of poweramplifiers based on the determined signal energies.
 2. The method ofclaim 1, wherein determining signal energies for the plurality ofsignals comprises analyzing the plurality of signals.
 3. The method ofclaim 2, wherein determining signal energies for the plurality ofsignals comprises computing respective sums of squared amplitudes forthe plurality of signals provided to the plurality of power amplifiers.4. The method of claim 1, wherein determining signal energies for theplurality of signals comprises analyzing the one or more beamsteeringmatrices.
 5. The method of claim 4, wherein determining signal energiesfor the plurality of signals comprises summing squared magnitudes ofmatrix coefficients in rows of the one or more steering matrices.
 6. Themethod of claim 4, wherein applying the one or more beamsteeringmatrices to the plurality of signals comprises applying a plurality ofbeamsteering matrices to the plurality of signals; wherein determiningsignal energies for the plurality of signals comprises summing squaredmagnitudes of matrix coefficients in rows of a subset of the pluralityof steering matrices.
 7. The method of claim 1, further comprisingcomparing the signal energies for the plurality of signals provided tothe plurality of power amplifiers; wherein adjusting the output powerlevels of the plurality of power amplifiers is based on comparisons ofthe signal energies.
 8. The method of claim 7, wherein comparing thesignal energies for the plurality of signals provided to the pluralityof power amplifiers comprises comparing one of the signal energies toeach of one or more other signal energies.
 9. The method of claim 8,wherein comparing the signal energies for the plurality of signalsprovided to the plurality of power amplifiers comprises: determining amaximum signal energy corresponding to one of the plurality of signals;and determining one or more ratios, comprising, for each of the one ormore other signals in the plurality of signals, determining a respectiveratio of the signal energy of the other signal to the maximum signalenergy; wherein adjusting the output power levels of the plurality ofpower amplifiers is based on the one or more ratios.
 10. The method ofclaim 9, wherein adjusting the output power levels of the plurality ofpower amplifiers comprises: setting an output power level of a poweramplifier corresponding to the maximum signal energy to a defined outputpower level; setting a corresponding output power level for each of oneor more additional power amplifiers to a corresponding power level basedon a corresponding determined ratio.
 11. The method of claim 10,wherein, for each of the one or more additional power amplifiers, thecorresponding power level is below the defined output power level. 12.The method of claim 10, wherein the defined output power level is amaximum output power level.
 13. The method of claim 7, wherein comparingthe signal energies for the plurality of signals provided to theplurality of power amplifiers comprises comparing each of the signalenergies to a reference signal energy.
 14. The method of claim 1,wherein adjusting the output power levels of the plurality of poweramplifiers comprising adjusting the output power levels of the pluralityof power amplifiers so that the relative output power levels correspondto the relative signal energies.
 15. The method of claim 1, whereinadjusting the output power levels of the plurality of power amplifierscomprising adjusting the output power levels of the plurality of poweramplifiers so that the output power levels are equal.
 16. A poweramplifier control apparatus, comprising a controller configured to:determine signal energies for a plurality of signals provided to aplurality of power amplifiers coupled to a plurality of transmitantennas, wherein one or more beamsteering matrices are applied to theplurality of signals; and generate control signals to adjust outputpower levels of the plurality of power amplifiers based on thedetermined signal energies.
 17. The apparatus of claim 16, wherein thecontroller receives the plurality of signals and is configured todetermine the signal energies for the plurality of signals based on ananalysis of the plurality of signals.
 18. The apparatus of claim 17,wherein the controller is configured to compute respective sums ofsquared amplitudes for the plurality of signals.
 19. The apparatus ofclaim 16, wherein the controller receives one or more beamsteeringmatrices and is configured to determine the signal energies for theplurality of signals based on an analysis of the one or morebeamsteering matrices.
 20. The apparatus of claim 19, wherein thecontroller is configured to sum squared magnitudes of matrixcoefficients in rows of the one or more steering matrices.
 21. Theapparatus of claim 19, wherein the one or more beamsteering matricescomprises a plurality of beamsteering matrices; wherein the controlleris configured to sum squared magnitudes of matrix coefficients in rowsof a subset of the plurality of steering matrices.
 22. The apparatus ofclaim 16, wherein the controller is configured to: compare the signalenergies for the plurality of signals provided to the plurality of poweramplifiers, and generate the control signals based on the comparison ofthe signal energies.
 23. The apparatus of claim 22, wherein thecontroller is configured to compare one of the signal energies to eachor one or more other signal energies.
 24. The apparatus of claim 23,wherein the controller is configured to: determine a maximum signalenergy corresponding to one of the plurality of signals; determine oneor more ratios, comprising, for each of the one or more other signals inthe plurality of signals, determining a respective ratio of the signalenergy of the other signal to the maximum signal energy; and generatethe control signals to adjust the output power levels of the pluralityof power amplifiers based on the one or more ratios.
 25. The apparatusof claim 24, wherein the controller is configured to: generate thecontrol signals to set an output power level of a power amplifiercorresponding to the maximum signal energy to a defined output powerlevel; and generate the control signals to set a corresponding outputpower level for each of one or more additional power amplifiers to acorresponding power level based on a corresponding determined ratio. 26.The apparatus of claim 24, wherein the controller is configured togenerate the control signals to set the corresponding power level foreach of the one or more additional power amplifiers to a correspondingpower level that is below the defined output power level.
 27. Theapparatus of claim 22, wherein the controller is configured to compareeach of the signal energies to a reference signal energy.
 28. Theapparatus of claim 16, wherein the controller is configured to adjustthe output power levels of the plurality of power amplifiers so that therelative output power levels correspond to the relative signal energies.29. The apparatus of claim 16, wherein the controller is configured toadjust the output power levels of the plurality of power amplifiers sothat the output power levels are equal.
 30. A wireless transmitter fortransmitting an information signal, the wireless transmitter comprising:a signal modulator adapted to modulate the information signal to producea modulated signal; a plurality of transmission antennas; a beamformingnetwork coupled between the signal modulator and the plurality oftransmission antennas; a first controller coupled to the beamformingnetwork to control the beamforming network using one or more steeringmatrices so as to produce a transmit gain pattern having one or morehigh gain lobes when the modulated signal is transmitted via theplurality of transmission antennas; a plurality of power amplifierscoupled to the beamforming network and the plurality of transmissionantennas; and a second controller coupled to the plurality ofamplifiers, the second controller configured to: determine signalenergies for a plurality of signals provided to the plurality of poweramplifiers, and generate control signals to adjust output power levelsof the plurality of power amplifiers based on the determined signalenergies.
 31. The wireless transmitter of claim 30, wherein the secondcontroller receives the plurality of signals; wherein the secondcontroller is configured to determine the signal energies for theplurality of signals based on an analysis of the plurality of signals.32. The wireless transmitter of claim 30, wherein the second controllerreceives one or more beamsteering matrices; wherein the secondcontroller is configured to determine the signal energies for theplurality of signals based on an analysis of the one or morebeamsteering matrices.
 33. The wireless transmitter of claim 32, whereinthe second controller is coupled to a steering matrix memory.
 34. Thewireless transmitter of claim 30, further comprising a steering matrixcalculation unit.
 35. The wireless transmitter of claim 30, wherein thesecond controller is configured to: compare the signal energies for theplurality of signals provided to the plurality of power amplifiers, andgenerate the control signals based on the comparison of the signalenergies.
 36. The wireless transmitter of claim 30, wherein the secondcontroller is configured to adjust the output power levels of theplurality of power amplifiers so that the relative output power levelscorrespond to the relative signal energies.
 37. The wireless transmitterof claim 30, wherein the second controller is configured to adjust theoutput power levels of the plurality of power amplifiers so that theoutput power levels are equal.
 38. A method of wirelessly transmittingan information signal via multiple antennas, the method comprising:modulating the information signal to produce a modulated signal;applying one or more beamsteering matrices to the modulated signal toproduce a plurality of output signals; providing the plurality of outputsignals to a plurality of power amplifiers, wherein the plurality ofpower amplifiers are coupled to the multiple antennas; determiningsignal energies for the plurality of output signals; and adjustingoutput power levels of the plurality of power amplifiers based on thedetermined signal energies.
 39. The method of claim 38, whereindetermining signal energies for the plurality of output signalscomprises analyzing the plurality of output signals.
 40. The method ofclaim 38, wherein determining signal energies for the plurality ofoutput signals comprises analyzing the one or more beamsteeringmatrices.
 41. The method of claim 38, further comprising comparing thesignal energies for the plurality of output signals; wherein adjustingthe output power levels of the plurality of power amplifiers is based oncomparisons of the signal energies.
 42. The method of claim 38, whereinadjusting the output power levels of the plurality of power amplifierscomprising adjusting the output power levels of the plurality of poweramplifiers so that the relative output power levels correspond to therelative signal energies.
 43. The method of claim 38, wherein adjustingthe output power levels of the plurality of power amplifiers comprisingadjusting the output power levels of the plurality of power amplifiersso that the output power levels are equal.